The invention relates to an electro-optic Mach-Zehnder modulator arrangement and a method for operating a Mach-Zehnder modulator arrangement.
It is known in the art to use Mach-Zehnder interferometers as electro-optic modulators in optical high-speed transmission systems, wherein, for example, coplanar travelling wave electrodes (TWE) are used to induce a phase shift in the interferometer arms. These TWEs comprise a first and a second coplanar microwave line connected to a plurality of periodically arranged and capacitively coupled electrodes on top of the waveguides. Examples of such TWE-Mach-Zehnder modulators are described in the publication “High-Speed III-V Semiconductor Intensity Modulators”, Robert G. Walker, IEEE Journal of Quantum Electronics Vol. 27, No. 3, March 1991.
Usually, a high frequency (e.g. >20 GHz) data signal is supplied to the Mach-Zehnder modulator via an amplifying driver, wherein a signal carrying connector of the driver is connected to one of the coplanar lines of the TWE, whereas the other coplanar line is grounded (single drive operation). Further, the impedance of the travelling wave electrode of the modulator is matched to the conventional 50 Ohm impedance of the output port of the driver. However, this asymmetric operation of the TWE creates stray capacitances against ground which may, for example, cause drops in the frequency response of the Mach-Zehnder modulator due to parasitic electrical modes.
In order to eliminate stray capacitances a complicated layout of the high frequency interface between the electric input port of the modulator and the coplanar line of the modulator as well as a complicated grounding of the modulator module is required. For example, the modulator housing is arranged at a great distance (for example, several millimeters) from the TWE.
Further, the publication “Advances in InP Mach-Zehnder modulators for large capacity photonic network systems”, H. Yasaka et al., Indium Phosphide and Related Materials, IPRM 2008, p. 1, discloses a Mach-Zehnder modulator having separate (electrically uncoupled) continuous electrodes disposed on the optical waveguides, wherein the electrodes are driven by two 50 Ohm drivers requiring twice the voltage of the capacitively coupled TWE.